For electronically controlling the operation of various devices on a vehicle, such as an internal combustion engine, an air conditioner, door mirrors, power windows and wipers, various electronic devices are mounted on the vehicle. In recent years, one vehicle is equipped with 50-60 units of such electronic devices, and the number of the on-vehicle electronic devices is increasing. Electronic devices such as controllers, or ECU's (Electronic Control Units) are connected to the bus of an on-vehicle LAN (Local Area Network), and transmit/receive data in accordance with protocols such as LIN (Local Interconnect Network), CAN (Controller Area Network), or CXPI (Clock Extension Peripheral Interface), etc.
Various problems may occur in data transmission/reception between on-vehicle electronic devices.